Psoas Abscess From Spinal Tuberculosis Mimicking Appendicitis: A Case Report

Osteoarticular tuberculosis (TB) is a form of extrapulmonary TB that affects bones and joints, with the spine being the most common site of involvement. Spinal TB, also known as Pott's disease, is therefore the most frequent manifestation of osteoarticular TB. Historically, Pott's disease has been more prevalent in developing countries; however, its incidence is increasing in developed nations, driven by global migration and a growing population of immunocompromised individuals. We report the case of a woman in her 50s who presented with a one- to two-month history of intermittent lower abdominal pain, radiating to the back and associated with fever, nausea, and recent weight loss. Initial examination suggested acute appendicitis, with tenderness localised to the right lower quadrant and McBurney's point. Laboratory investigations revealed mild anaemia (haemoglobin, or Hb 95 g/L) and elevated C-reactive protein (CRP) (49 mg/L), while other parameters were normal. Computed tomography (CT) imaging revealed a large left psoas collection with vertebral destruction at L4, suggestive of discitis/osteomyelitis. Magnetic resonance imaging (MRI) confirmed a multiloculated left psoas abscess with extensive involvement of the L4/L5 vertebrae, paravertebral tissues, and epidural space. CT-guided aspiration obtained approximately 90 mL of pus, which tested positive for <i>Mycobacterium tuberculosis</i> without rifampicin resistance. Initial empiric therapy with flucloxacillin was discontinued, and antitubercular therapy was commenced. Subsequent drug susceptibility testing revealed isoniazid resistance, prompting regimen modification to include rifampicin, pyrazinamide, ethambutol, and levofloxacin. The patient improved clinically, with gradual resolution of symptoms and reduction in abscess size on follow-up imaging. Multidisciplinary management, involving general surgery, radiology, microbiology, and infectious disease teams, was critical for timely diagnosis and tailored therapy. This case highlights the atypical presentation of spinal TB with a left-sided psoas abscess mimicking acute appendicitis. It also shows the importance of a multidisciplinary approach, early imaging, CT-guided aspiration for microbiological confirmation, and culture-guided therapy, especially in the context of drug-resistant TB. Awareness of such presentations can prevent diagnostic delays, reduce morbidity, and optimise outcomes.